Abstract
Increasing atmospheric nitrogen (N) deposition has a profound impact on the ecosystem functions and processes. Fine root decomposition is an important pathway for the reentry of nutrients into the soil. However, the effect of N addition on root decomposition and its potential mechanism is not well understood with respect to root branch orders. In this study, we conducted a 30-month decomposition experiment of fine roots under different concentrations of N addition treatments (0, 30, 60, and 90 kg N ha -1 year -1 , respectively) in a typical Pinus massoniana plantation in the Three Gorges Reservoir Area of China. In the early stage of decomposition (0−18 months), N addition at all concentrations promoted the decomposition of fine roots, and the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively. In the late stage of decomposition (18−30 months), high N addition inhibited the decomposition of fine root, and the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively. At the same time, N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage, whereas high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage. The decomposition constant ( k ) was significantly correlated with the initial chemical quality of the fine roots and lignin-degrading enzyme activities. The higher-order (order 3–4 and order 5–6) fine roots decomposed faster than lower-order (order 1–2) fine roots due to higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrations. In addition, low N (30 kg N ha -1 year -1 ) treatments decreased soil organic matter content, whereas high N (90 kg N ha -1 year -1 ) treatment had the opposite effect. All the N treatments reduced soil pH and total P content, indicating that increased N deposition may led to soil acidification. Our findings indicated that the effect of N addition on decomposition varied with the decomposition stages. The decomposition difference between the lower-order and higher-order fine roots were controlled strongly by the initial chemical quality of the fine roots. This study provides new insights into understanding and predicting possible changes in plant root decomposition and soil properties in the future atmospheric N deposition increase scenarios.
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Claims 17
Claim · model-written summary
Early-stage (0-18 months) N addition at all concentrations increased the average decomposition rate of order 1-2 fine roots of Pinus massoniana by 13.54%.
- Taxon
- Pinus massoniana
Pinus massonianat0 - Organ / stage
- order 1–2e1
- Treatment
- N addition at all concentrationse0
- Outcome
- average decomposition ratese1
- Direction
- increasede1
- Value
- 13.54%e1
- Qualifier
- early stage of decomposition (0−18 months)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e0“In the early stage of decomposition (0−18 months), N addition at all concentrations”
e1“the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively”
Claim · model-written summary
Early-stage (0-18 months) N addition at all concentrations increased the average decomposition rate of order 3-4 fine roots by 6.15%.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- order 3–4e1
- Treatment
- N addition at all concentrationse0
- Outcome
- average decomposition ratese1
- Direction
- increasede1
- Value
- 6.15%e1
- Qualifier
- early stage of decomposition (0−18 months)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e0“In the early stage of decomposition (0−18 months), N addition at all concentrations”
e1“the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively”
Claim · model-written summary
Early-stage (0-18 months) N addition at all concentrations increased the average decomposition rate of order 5-6 fine roots by 7.96%.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- order 5–6 fine rootse1
- Treatment
- N addition at all concentrationse0
- Outcome
- average decomposition ratese1
- Direction
- increasede1
- Value
- 7.96%e1
- Qualifier
- early stage of decomposition (0−18 months)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e0“In the early stage of decomposition (0−18 months), N addition at all concentrations”
e1“the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively”
Claim · model-written summary
Late-stage (18-30 months) high N addition decreased the average decomposition rate of order 1-2 fine roots by 58.35%.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- order 1–2e1
- Treatment
- high N additione0
- Outcome
- average decomposition ratese1
- Direction
- decreasede1
- Value
- 58.35%e1
- Qualifier
- late stage of decomposition (18−30 months)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e0“In the late stage of decomposition (18−30 months), high N addition”
e1“the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively”
Claim · model-written summary
Late-stage (18-30 months) high N addition decreased the average decomposition rate of order 3-4 fine roots by 35.43%.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- order 3–4e1
- Treatment
- high N additione0
- Outcome
- average decomposition ratese1
- Direction
- decreasede1
- Value
- 35.43%e1
- Qualifier
- late stage of decomposition (18−30 months)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e0“In the late stage of decomposition (18−30 months), high N addition”
e1“the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively”
Claim · model-written summary
Late-stage (18-30 months) high N addition decreased the average decomposition rate of order 5-6 fine roots by 47.56%.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- order 5–6 fine rootse1
- Treatment
- high N additione0
- Outcome
- average decomposition ratese1
- Direction
- decreasede1
- Value
- 47.56%e1
- Qualifier
- late stage of decomposition (18−30 months)e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e0“In the late stage of decomposition (18−30 months), high N addition”
e1“the average decomposition rates of order 1–2, order 3–4, order 5–6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively”
Claim · model-written summary
In the early stage, N addition promoted the release of lignin, carbon and nitrogen from decomposing fine roots.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- N additione1
- Outcome
- release of lignin, carbon (C), Ne1
- Direction
- promotede1
- Qualifier
- early-stagee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage”
Claim · model-written summary
In the early stage, N addition promoted the release of phosphorus from decomposing fine roots.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- N additione1
- Outcome
- phosphorus (P)e1
- Direction
- promotede1
- Qualifier
- early-stagee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage”
Claim · model-written summary
In the late stage, high N addition inhibited the release of lignin, carbon and nitrogen from decomposing fine roots.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- high N additione1
- Outcome
- release of lignin, C, Ne1
- Direction
- inhibitede1
- Qualifier
- late-stagee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage”
Claim · model-written summary
In the late stage, high N addition inhibited the activities of the lignin-degrading enzymes peroxidase and polyphenol oxidase.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- high N additione1
- Gene
- peroxidase and polyphenol oxidasee1
- Outcome
- activities of lignin-degrading enzymee1
- Direction
- inhibitede1
- Qualifier
- late-stagee1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage”
Claim · model-written summary
The decomposition constant k was significantly correlated with the initial chemical quality of the fine roots and with lignin-degrading enzyme activities.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- fine rootse1
- Gene
- lignin-degrading enzymee1
- Outcome
- decomposition constant ( k )e1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“The decomposition constant ( k ) was significantly correlated with the initial chemical quality of the fine roots and lignin-degrading enzyme activities”
Claim · model-written summary
Higher-order (order 3-4 and 5-6) fine roots decomposed faster than lower-order (order 1-2) fine roots.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- higher-order (order 3–4 and order 5–6) fine rootse1
- Outcome
- decomposed fastere1
- Direction
- fastere1
- Comparator
- lower-order (order 1–2) fine rootse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“The higher-order (order 3–4 and order 5–6) fine roots decomposed faster than lower-order (order 1–2) fine roots”
Claim · model-written summary
The faster decomposition of higher-order fine roots is attributed to higher initial cellulose, starch, sugar and C concentrations, higher C/N, C/P and lignin/N ratios and lower N and P concentrations.
- Taxon
- Pinus massonianaPinus massonianat0
- Organ / stage
- higher-order (order 3–4 and order 5–6) fine rootse1
- Outcome
- decomposed fastere1
- Qualifier
- higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrationse1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“The higher-order (order 3–4 and order 5–6) fine roots decomposed faster than lower-order (order 1–2) fine roots due to higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrations”
Claim · model-written summary
Low N addition (30 kg N ha-1 year-1) decreased soil organic matter content.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- low N (30 kg N ha -1 year -1 )e1
- Outcome
- soil organic matter contente1
- Direction
- decreasede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“low N (30 kg N ha -1 year -1 ) treatments decreased soil organic matter content”
Claim · model-written summary
High N addition (90 kg N ha-1 year-1) had the opposite effect on soil organic matter content to low N.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- high N (90 kg N ha -1 year -1 )e1
- Outcome
- soil organic matter contente1
- Direction
- opposite effecte1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“low N (30 kg N ha -1 year -1 ) treatments decreased soil organic matter content, whereas high N (90 kg N ha -1 year -1 ) treatment had the opposite effect”
Claim · model-written summary
All the N treatments reduced soil pH and total P content.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- All the N treatmentse1
- Outcome
- soil pH and total P contente1
- Direction
- reducede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“All the N treatments reduced soil pH and total P content”
Claim · model-written summary
The authors suggest that increased N deposition may lead to soil acidification.
- Taxon
- Pinus massonianaPinus massonianat0
- Treatment
- increased N depositione1
- Outcome
- soil acidificatione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Pinus massoniana”
e1“increased N deposition may led to soil acidification”